1. Field of the Invention
The present invention relates to a stable heterogeneous catalyst capable of being used for hydrogenation, a method of preparing the same, and a method of hydrogenating a biomass-derived hydrocarbon compound using the heterogeneous catalyst, which is able to produce high-value-added chemicals by defunctionalizing a biomass (desorption of a functional group).
2. Discussion of Related Art
With the exhaustion of fossil fuels, biomasses have attracted attention as alternative fuels. The use of catalysts having two metals supported therein is effective in converting a biomass into much valuable chemicals by defunctionalizing the biomass (desorption of a functional group). However, it is difficult to prepare such heterogeneous catalysts under the control at a molecular level.
Aromatic carbon-based graphene is known to be used as a support for heterogeneous catalysts. This is due to the electrical, optical, thermal, mechanical characteristics of graphene, and carbon nanostructures associated with graphene. Among various kinds of graphene, a graphene oxide (hereinafter abbreviated as ‘GO’) exhibiting good dispersibility has been widely used since it can be prepared using the simplest synthesis methods. GO can be used as a catalyst since it functions as a support for nano-materials due to many functional groups and a wide area. Up to now, GO has been used as a catalyst after being bound to metals, metal oxides, semiconductors, or magnetic nano-materials.
However, when the metals, metal oxides, semiconductors or magnetic nano-materials are supported in GO, it is impossible to ensure stability as a support.
Meanwhile, a hydrogen fuel is a clean fuel which produces no pollutants such as carbon dioxide while generating a great amount of energy upon combustion. However, since it is difficult to produce, store and transport the hydrogen fuel, it has not yet been able to replace the conventional fossil fuels. In recent years, hydrogen has been increasingly consumed, and 84% of the fossil fuels have been used after petroleum is purified by removing elements such as oxygen, nitrogen and sulfur. Also, a synthesis procedure such as preparation of drugs requires at least one hydrogenation operation. Although it is apparent that hydrogen is a valuable material, the use of hydrogen is limited due to difficulty in handling and high risk of explosion. Therefore, there is a demand for development of a method by which hydrogen can be directly produced in a reactor and simultaneously used for a hydrogenation reaction rather than a method of injecting hydrogen gas from the outside upon purification of petroleum and the hydrogenation reaction. In light of this, since one molecule of hydrogen and one molecule of carbon dioxide are produced by decomposition of formic acid, formic acid has attracted attention as a liquid source for producing hydrogen.
To decompose formic acid, homogeneous or heterogeneous catalysts are required. Among these, the homogeneous catalysts have a problem in that they are not easily separated from products after a reaction, and the heterogeneous catalysts have a problem in that their activities decreases with an increase in reaction time since metal nanoparticles are used as the heterogeneous catalysts. Also, the severe conditions for decomposition of formic acid promote detachment of a metal catalyst from a GO support.
As one example of the prior-art documents associated with these techniques, Korean Unexamined Patent Publication No. 10-2013-0074904 (published on Jul. 5, 2013) discloses catalysts which include a graphene oxide support and at least one functional group selected from the group consisting of carboxylic acid, sulfonic acid and phosphoric acid, the functional group being supported in the graphene oxide support, especially catalysts suitable for preparation of levulinic acid or ester compounds thereof derived from biomasses.
As another example of the prior-art documents, Korean Unexamined Patent Publication No. 10-2013-0079389 (published on Jul. 10, 2013) disclosed a method of preparing a biofuel which involves treating an organic matter with an aqueous solvent and one or more catalysts at a temperature of 250° C. to 400° C. and a pressure of 100 bar to 300 bar. Here, at least one catalyst selected from the group consisting of an alkali metal formate catalyst, a transition metal formate catalyst, a reactive carboxylic acid catalyst, a transition metal catalyst, a sulfide catalyst, a noble metal catalyst, a water-gas transfer catalyst, and a combination thereof may be used as the catalyst for promoting introduction of hydrogen, and at least one catalyst selected from the group consisting of an acid catalyst, a transition metal catalyst, a noble metal catalyst, a supported transfer metal catalyst, a solid acid catalyst, and a mixture thereof may be used as the catalyst for promoting removal of oxygen from an organic matter.
In addition, Korean Unexamined Patent Publication No. 10-2013-0012900 (published on Jan. 5, 2013) disclose a catalyst including inorganic nanoparticles coated with an organic ligand and a graphene oxide nanosheet for supporting the inorganic nanoparticles, wherein the catalyst exhibits high catalytic activities in a reduction of a nitroarene-based compound and has improved catalyst stability.
By way of example, the catalysts disclosed in the above-described prior-art documents show high selectivity and satisfactory conversion rates, but have problems in that the catalytic activities may be degraded upon recovery and repeated recycling after a hydrogenation reaction. Further, there is no report on the functions of catalysts applicable to two continuous procedures such as generation of hydrogen by decomposition of formic acid and application of hydrogen to a hydrogenation reaction.
Meanwhile, much research is being conducted recently on preparing biofuels. One typical example is defunctionalization of vanillin (desorption of a functional group). However, catalytic reactions reported in the prior art occur under the certain conditions (50 psi, 100° C. or 1 mPa, 90° C.: Journal of the American Chemical Society 134, 16987-16990, 2012) in which pressurization has to be realized by directly supplying hydrogen from the outside.